Method of tanning hides and skins



Patented Mar. 5, H335 UNITED STATES PATENT OFFICE 7 1,993,298 DIETHOD 0F TANNING HIDES AND SKINS No Drawing. Application April 12, 1934, Serial No. 720,211

13 Claims.

This invention relates to methods of tanning hides and skins. While the invention is described with reference to the chrome tanning of sheepskins it will be understood that the invention and various important characteristics thereof may have other applications and uses.

It is an object of the invention to improve, in certainrespects, upon the method disclosed in United States Letters Patent No. 1,852,996, granted April 5, 1932, upon an application filed in my name on January 12, 1931. According to the patented method, skins from the pickle begin the tanning operation by being first subjected to a tanning agent which is either non-tanning in I itself or of only moderate tanning effect within the time allotted. Following this treatment the skins are thoroughly slicked out upon a smooth work supporting surface, thus securing elimination of all wrinkles and folds and a marked increase in area over that of the pickled skin. While maintained in this fully slicked-out condition the skins are treated with a reducing agent which, in conjunction with the. tanning agent first applied, produces a tanning combination effective under proper conditions to tan the skins thoroughly. After the application of the reducing agent the skins remain in extended condition for a definite length of time, substantially just suflicient to secure setting of the skins or a partial tanning thereof, whereby they will retain their extended area while undergoing completion of the tanning operation after removal from the said work supporting surface.

I have found that even better results are obtained if; following a more or less prolonged treatment of the skins by a reducing agent while the skins are in fully extended condition, they are then reintroduced into a drum and tumbled therein without the introduction of treating liquid of any kind. Preferably the drum is arranged so that liquid may escape, during the tumbling operation which may, on this account,

be termed dry drumming, although the skins are not dry but quite wet with the tanning and reducing solutions at the beginning ofthe-tumbling operation. The dry drumming operation is particularly advantageous in that it secures uniform distribution of the tanning and reducing materials which have been applied to the skins and also contributes an added quality of softness and flexibility to the skins. Furthermore, as a matter of marked importance, the skins following this dry drumming operation may be readily slicked out in such manner as to obtain the full area secured in the first slickingout operation and to leave no wrinkles or folds in the skins. Following the dry drumming and the second spreading-out or slicking-out operations, the skins are allowed to remain stacked in flat spread-out or slicked-out condition for several hours during which the tanning material effects completion of the tanning operation by setting the chromium compounds in and upon the fibres of the skin. The skins are then se- 10 cured to drying boards without any stretching thereof and allowed to dry.

The above and other important characteristics of the invention will now be described in detail in the specification and then pointed out more 15 particularly in the appended claims.

In the practice of the method, sheepskins in the amount of ten to fifteen dozen are introduced into a freely ventilated drum about-four feet in diameter and four feet in length along its axis of rotation, the drum being relatively small to minimize pounding of the skins and to make possible the use of small amounts of tanning liquor. Intothis drum there is introduced with the skins a tanning liquid in the amount of three-quarters of a gallon to each dozen skins. For ten dozen sheepskins there is used, for example, three hundred ounces of a basic chromium sulphate, eighty ounces of commercial sulphuric acid, and eighty ounces of commercial sodium dichromate dissolved in water to provide about seven and one-half gallons of liquor for the ten dozen skins. In this liquor the skins are drummed for about one hour. Since all or most of the basic chromium sulphate is changed to the normal surphate by the sulphuric acid pres ent, little or no tanning of the skins is effected by the described drumming operation. At any rate, it is certain that the relatively short drumming in the described solution does not prevent the skins from being stretched out in fully extended condition by the spreading or slicking operation which follows the removal of the skins from the drum. 5

In the slicking-out operation, the skins are placed grain surface down upon flexible mats which may be of rubber, rubber composition, or of linoleum or any other substance suitable for the purpose. As soon as the skin is slicked 50 out on a flexible mat, a solution (about 200 Bkr.) of thiosulphate of sodium, ordinarily known as hypo, is applied to the exposed flesh surface as, for instance, by swabbing. The mat with its slicked-out skin is then turned over I with the skin flesh side down upon a setting board after which the flexible mat is peeled or stripped from the skin, leaving it in fully extended condition on the setting board. Commonly, a number of similarly treated skins are placed one upon another until a dozen or more are in a pile upon one setting board. As each skin is placed upon the setting board, additional hypo is applied to the exposed grain surface, it being recalled that the first application of hypo was-to the flesh surface. The skins are allowed to remain in this pile for the action of the hypo during a period of about two hours as a minimum, although they may be left overnight if desired. This setting over a period of hours takes the place of the horsing up of the skins in prior methods and has the distinct advantages of maintaining the skins in extended condition during setting thereof and of securing much more even draining, since skins left to set on a horse drain much more in the flanks and bellies and very unevenly at that.

In the next step of the process, the skins are removed from the setting board and reintroduced into the drum in which they are tumbled under conditions which permit the skins to drain. In other words; no treating liquid of any kind is added but on the contrary liquid may escape during the tumbling operation. This operation of dry drumming has the effect of securing complete uniformity in the distribution of the chrome tanning and reducing solutions throughout the substance of the skins undergoing treatment. Furthermore, this drumming has the advantage of securing a high quality of softness and flexibility in the skins so treated, and may advantageously be employed in the treatment of skins which have received a tanning treatment different from that herein described. For example, skins which have been drummed in the usual one-bath or two-bath solutions, and then horsed up overnight, may then be dry drummed with excellent results.

At the end of a period which may be as long as one hour of dry drumming, the skins are thoroughly washed with pure water in the same drum which is preferably so constructed as to permit the escape of water at one point while fresh water is entering at another point. At this time, also, the skins may be colored with wattle or dyed with any of the well-known dyeing preparations, and then fatliquored if desired, without removing them from the drum in which they were tumbled and washed.

Following the washing a'nd/or coloring operations, the skins are taken from the drum and slicked out, grain surface down, upon a flexible mat and piled as before, each in fully extended condition upon a setting board, one or two dozen skins to the board, where they are allowed to set overnight. While this period of setting may be only a few hours in length, the overnight period appears to have decided advantages. In the latter case, a covering sheet of impervious paper or "the like may be used to advantage to prevent undue evaporation from the top skin or skins. The skins should be allowed to set until they have become firm in texture and have lost their flaccid condition. This period of setting in fully extended condition after the application of the reducing agent is most important, for during this time there takes place fixation of the chromium compounds upon and in the fibres of the skin. In this manner, the tanning operation is practically completed.

These skins are then lifted to individual drying boards upon which they will rest in fully extendedcondition without any stretching being necessary. They are secured to the drying boards with a relatively small number of securing devices, such as light wire staples, and left to dry with the drying boards hung up in a room without the provision of any special means to secure drying. In other words, the skins are allowed to dry at ordinary room temperatures.

It is desired to emphasize again that, in the first slicking-out operation the skins are easily slicked out to obtain all the area which may be reasonably obtained without undue stretching of any part. Furthermore, every wrinkle and fold of the skin is removed in the slicking operation, this result being obtainable for the reason that the' skins are not tanned by the drumming with the first tanning material which is either non-tanning or of very. little tanning effeet in the short period during which the treatment is carried out. In the second slicking-out operation, the skins are also spread out in such manner as to remove any wrinkles or folds, since no wrinkles or folds were tanned in the skins at the time the hypo was applied as a reducing agent, first to the flesh surface and then to the grain surface of each skin following the first slicking-out operation. Because of the slickingout operations followed by the periods of setting in extended condition during the action of the tanning materials, the skins, when they come to the drying boards, do not need any stretching as they are already in wholly spread-out or slickedout condition and need only be attached to the drying boards as a preliminary to being suspended for the drying operation.

Having described my invention, what I claim 5 as new and desire to secure by Letters Patent of the United States is:

1. That improvement in methods of tanning skins which comprises subjecting the skins to treatment with tanning solutions until such solutions have fully penetrated the skins, maintaining the skins in fully extended condition until the tanning has proceeded far enough to set the skins, and then dry-drumming the wet skins.

2.'That improvement in methods of tanning skins which comprises subjecting the skins to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, maintaining the skins spread out in fully extended condition upon a smooth work supporting surface for a time sufficient to secure such a setting thereof in extended condition as will maintain the area of the skin during subsequent operations, then dry-drumming the skins while still wet with the tanning solutions, and then spreading the skins out in fully extended condition to remain until they become firm in texture and completely tanned. v

3. That improvement in-methods of tanning skins which comprises subjecting the skins to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, maintaining the skins spread out in fully extended condition for a time sufficient to secure such a setting thereof as will maintain the area of the skins during subsequent operations, then dry drumming these skins while still wet with the tanning solutions to effect uniform distribution of the tanning material throughout the substance of the skins undergoing treatment and to secure softness and flexibility in the finished prod-' not, and then slicking the skins out upon a smooth supporting surface.

4. That improvement in methods of taming skins which comprises subjecting the skins to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, removing a large part of the spent tanning solution from the skins and allowing them to remain in extended condition in a pile for several hours, dry drumming these skins while still wet with the tanning solutions, then slicking the skins out upon a smooth supporting surface, and stacking the slicked-out skins in fiat extended condition in a pile to remain until they become firm in texture and completely tanned.

5. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, re-

moving a large part of the spent tanning solution from the skins and allowing them to remain in extended condition in a pile for several hours, dry drumming these skins while still wet with the tanning solutions, and draining the skins simultaneously with the drumming thereof.

6. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, piling the skins over a horse to remove a large part of the spent tanning solution therefrom by pressure and drainage, allowing them to remain in extended condition in the pile for several hours, dry drumming these skins while still wet with the tanning solutions, slicking the skins out upon a smooth supporting surface, and stacking the skins in their slicked-out condition in a flat pile to remain until they become firm in texture and completely tanned.

'7. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by a chrome tanning solution until such material has fully penetrated each skin, then promptly slicking the skin out in fully extended condition upon a smooth work supporting surface, the skins being allowed to remain in extended condition on a work supporting surface for a time substantially just sufficient to secure such a setting thereof as will maintain the area of the skin during subsequent operations, dry drumming the skins while still wet with the tanning solution, and then again slicking the skins out upon a smooth supporting surface to remain in slicked-out condition until they become firm in texture and completely tanned.

8. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by a tanning solution, which in itself is non-tanning, until such agent has fully penetrated each skin, then slicking the skin out in fully extended condition upon a smooth work supporting surface, treating the skin while it is maintained in such fully extended condition with another tanning agent which, in conjunction withthe first-mentioned tanning solution, provides for effective tanning of the skin, the skins being allowed to remain on the work supporting surface after the application of the second tanning agent for a time substantially just sufiicient to secure such a setting thereof as will maintain the area of the skin during subsequent operations, dry drumming the skins while still wet with the tanning solution, again slicking the skins out upon a smooth supporting surface, and piling the skins in stacks to remain until they become firm in texture and completely tanned.

9. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by a tanning agent, which in itself is non-tanning, until such agent has fully penetrated each skin, then slicking the skin out in fully extended condition upon a smooth work supporting surface, treating the skin while it is maintained in such fully extended condition with another tanning agent which, in conjunction with the first-mentioned tanning agent, provides for efiective tanning of the skin, the skins being allowed to remain on the work supporting surface after the application of the second tanning agent for a time substantially just suflicient to secure. such a setting thereof as will maintain the area of the skin during subsequent, operations, then drumming these skins without the addition of any treating substance to effect uniform distribution of the tanning material throughout the substance of the skin undergoing treatment, draining the skins simultaneously with the drumming thereof, then againslicking the skins out upon a smooth supporting surface, and stacking the skins in their slicked-out condition to remain until they become firm in texture and completely tanned.

10. That improvement in methods of tanning skins which comprises subjecting the skins in fully spread-out condition to treatment by chrome tanning solutions until such solutions have fully penetrated each skin, piling the treated skins one on another in fully extended condition, covering the pile of skins with a sheet of moisture-proof material to prevent evaporation, and allowing them to remain in the pile to effect uniform distribution of the tanning material throughout the substance of the skins undergoing treatment and to become firm in texture and completely tanned.

11. That improvement in methods of tanning skins which comprises subjecting the skins in fully spread-out condition to treatment by tanning solutions until such solutions have fully penetrated each skin, the skins being allowed to remain in extended condition on a work supporting surface for a time substantially just sufllcient to secure such a setting thereof as will maintain the area of the skin during subsequent operations, and stacking the skins on a support until a dozen or more skins are in extended condition on said support where they are allowed to remain until they become firm in texture and completely tanned.

12. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by a tanning agent, which in itself is non-tanning, until such agent has fully penetrated each skin, then slicking the skin out in fully extended condition upon a smooth work supporting surface, treating the skin while it is maintained in such fully extended condition with another tanning agent which, in conjunction with the first-mentioned tanning agent, provides for effective tanning of the skins, transferring the skin in extended condition to a flat support, repeating these operations on other skins and stacking the skins on the support until a dozen or more skins are in extended condition in a stack on said support, and leaving the skins to set on the support for a number of hours, whereby they become thoroughly tanned in extended flat condition.

13. That improvement in methods of tanning skins which comprises subjecting the skins to treatment by a chrome tanning agent, which in itself is non-tanning, until such agent has fully penetrated each skin, then shaking the skin out 5 in fully extended condition upon a smooth work supporting surface, treating the skin while it is maintained in such fully extended condition with a reducing agent which, in conjunction with the chrome tanning agent, provides for effective 10 tanning of the skin, reversing the skin in its fully extended condition upon a flat support, applying more of the reducing agent to the newly exposed surface of the skin, repeating these operations on a number of skins and stacking them until about a dozen skins are stacked on said flat sup port, and leaving them in the stack for a number of hours to become thoroughly tanned 1n extended fiat condition. 

